The present invention relates to an electrical contact pin having a mounting portion to be fitted into a plated through hole (PTH) of a circuit board without using any solder.
Electrical contact pins of such a type are sometimes called "press fit contactors" and disclosed in for example in U.S. Pat. Nos. 4,223,970 issued to Leo Walter on Sept. 23, 1980, and 4,464,009 to Hartmuth Thaler on Aug. 7, 1984, and Japanese Pat. Kokai No. 58-123,678.
Walter Patent discloses a compliant backplane electrical connector having a pin with four edges at the corners of the generally rectangular, Z-shaped cross section of the pin. Such edges penetrate the plating of an opening upon insertion of the pin into the opening.
The Thaler Patent discloses a solderless connector pin for electrical circuits. It has an elongated deformable region having an M-shaped or W-shaped cross section. Upon insertion of the pin into a bore, the deformable region deforms elastically and, in the case of a small diameter bore, partially plastically to provide a good electrical and mechanical connection between the pin and the plating.
Japanese Pat. No. 58-123,678 discloses, as shown in FIG. 6(D), a contact pin consisting of a mounting portion 1 having an N-shaped cross section with a pair of triangular recesses 2 and 3 arranged in an alternating fashion on opposite sides. In order that corners 4 and 5 adjacent to these triangular recesses fully abut the conductive through hole of a circuit board, the opposite corners of the terminal are rounded to form chamfers 6 and 7. The mounting portion 1 of contact pin 9 with such structure has a springy accordion-like property.
One method of manufacturing such contact pins with the aid of a press machine will be described.
(1) As FIG. 6(A) shows, upper and lower metal dies 20 and 30 have triangular projections 21 and 31 to form the triangular recesses 2 and 3 and rounded corners 22 and 32 to form chamfers 6 and 7, respectively, of a metallic work or mounting portion 1.
(2) These dies are mounted on a press machine and pressed against the metal work 1 in the vertical direction. As FIG. 6(B) shows, as a result, indefinite burrs or fins 2' and 3' of excess material are produced because of the presence of triangular projections 21 and 31 and rounded corners 22 and 32.
(3) As FIG. 6(C) shows, these undesired burrs or fins 2' and 3' of excess material are cut off by a pair of press cutters 22 and 33.
(4) As FIG. 6(D) shows, finally, a mounting portion having an N-shaped cross section is completed.
Electrical contact pins having such a springy accordion-like mounting portion as described above have been developed so as to fit into PTHs in a certain range of diameters of a circuit board. However, they still have the following disadvantages:
(1) Where the diameter of a PTH is relatively large, although the corners 4 and 5 adjacent to the triangular recesses can abut the conductive wall of a PTH making electrical connection, the other rounded corners or chambers 6 and 7 cannot abut the conductive wall, because the diameter between the rounded corners 6 and 7, which is smaller than that between the corners 4 and 5, is smaller than the relatively large PTH diameter, thus as a whole making poor connection and increasing contact resistance especially after a vibration or shock has been applied for a long period of time.
(2) Where the diameter of a PTH is relatively small, the non-springy chamfers 6 and 7 strongly abut the conductive wall (solder layer) and severely damage it, thus increasing contact resistance or making conduction impossible because of complete separation of the conductive wall from the PTH.
(3) The indefinite burrs or fins 2' and 3' formed in the pressing step are so small that it is a difficult operation to cut them off. In addition, the resulting cuts become broken surfaces 6b and 7b as shown in FIG. 6(D) making the corners 4 and 5 imperfect or too short to penetrate the conductive wall of a PTH or reducing the accordion-like spring force of the corners.